1. Field of the Invention
The present invention relates to post-tension anchor systems. More particularly, the present invention relates to anchors used in such systems. More particularly, the present invention relates to affixing a tendon within an anchor of such systems. Additionally, the present invention relates to affixing a sheathing of a tendon within an anchor of such systems.
2. Description of Related Art Including Information Disclosed Under 37 CFR 1.97 and 37 CFR 1.98
For many years, the design of concrete structures imitated the typical steel design of column, girder and beam. With technological advances in structural concrete, however, concrete design began to evolve. Concrete has the advantages of costing less than steel, of not requiring fireproofing, and of having plasticity, a quality that lends itself to free flowing or boldly massive architectural concepts. On the other hand, structural concrete, though quite capable of carrying almost any compressive load, is weak in carrying significant tensile loads. It becomes necessary, therefore, to add steel bars, called reinforcements, to concrete, thus allowing the concrete to carry the compressive forces and the steel to carry the tensile forces.
Structures of reinforced concrete may be constructed with load-bearing walls, but this method does not use the full potentialities of the concrete. The skeleton frame, in which the floors and roofs rest directly on exterior and interior reinforced-concrete columns, has proven to be most economic and popular. Reinforced-concrete framing is seemingly a simple form of construction. First, wood or steel forms are constructed in the sizes, positions, and shapes called for by engineering and design requirements. The steel reinforcing is then placed and held in position by wires at its intersections. Devices known as chairs and spacers are used to keep the reinforcing bars apart and raised off the form work. The size and number of the steel bars depends completely upon the imposed loads and the need to transfer these loads evenly throughout the building and down to the foundation. After the reinforcing is set in place, the concrete, comprising a mixture of water, cement, sand, and stone or aggregate and having proportions calculated to produce the required strength, is set, care being taken to prevent voids or honeycombs.
One of the simplest designs in concrete frames is the beam-and-slab. This system follows ordinary steel design that uses concrete beams that are cast integrally with the floor slabs. The beam-and-slab system is often used in apartment buildings and other structures where the beams are not visually objectionable and can be hidden. The reinforcement is simple and the forms for casting can be utilized over and over for the same shape. The system, therefore, produces an economically viable structure. With the development of flat-slab construction, exposed beams can be eliminated. In this system, reinforcing bars are projected at right angles and in two directions from every column supporting flat slabs spanning twelve or fifteen feet in both directions.
Reinforced concrete reaches its highest potentialities when it is used in pre-stressed or post-tensioned members. Spans as great as five hundred feet can be attained in members as deep as three feet for roof loads. The basic principle is simple. In pre-stressing, reinforcing rods of high tensile strength wires are stretched to a certain determined limit and then high-strength concrete is placed around them. When the concrete has set, it holds the steel in a tight grip, preventing slippage or sagging. Post-tensioning follows the same principle, but the reinforcing tendon, usually a steel cable, is held loosely in place while the concrete is placed around it. The reinforcing tendon is then stretched by hydraulic jacks and securely anchored into place. Pre-stressing is done with individual members in the shop and post-tensioning as part of the structure on the site.
In a typical tendon tensioning anchor assembly used in such post-tensioning operations, there are provided anchors for anchoring the ends of the cables suspended therebetween. In the course of tensioning the cable in a concrete structure, a hydraulic jack or the like is releasably attached to one of the exposed ends of each cable for applying a predetermined amount of tension to the tendon, which extends through the anchor. When the desired amount of tension is applied to the cable, wedges, threaded nuts, or the like, are used to capture the cable at the anchor plate and, as the jack is removed from the tendon, to prevent its relaxation and hold it in its stressed condition.
In typical post-tension systems, the tendon is received between a pair of anchors. One of the anchors is known as the “live end” anchor, and the opposite end is known as the “dead-end” anchor. The “live end” anchor receives the end of the tendon which is to be tensioned. The “dead-end” anchor holds the tendon in place during the tensioning operation. Under typical operations, a plurality of wedges are inserted into an interior passageway of the anchor and around the exterior surface of the tendon. The tendon is then tensioned so as to draw the wedges inwardly into the interior passageway so as establish compressive and locking contact with an exterior surface of the tendon. This dead-end anchor can then be shipped, along with the tendon, for use at the job site.
One technique for forming such dead-end anchors is to insert the end of a tendon into the cavity of the anchor, inserting wedges into the space between the tendon and the wall of the cavity and then applying a tension force onto another end of the tendon so as to draw the wedges and the end of the tendon into the cavity in interference-fit relationship therewith. This procedure is somewhat difficult since the tendon can have a considerable length and since the use of tension forces can create a somewhat unreliable connection between the wedges and the tendon. Experimentation has found that the application of compressive force onto the end of the tendon creates a better interference-fit relationship between the wedges, the end of the tendon and the wall of the cavity of the anchor.
Various patents have addressed the creation of dead-end anchorages. For example, U.S. Pat. No. 6,513,287, issued on Feb. 4, 2003 to the present inventor, discloses a method and apparatus for forming an anchorage of a post-tension system in which a tendon is positioned within a cavity of an anchor such that an end of the tendon extends outwardly of the cavity, a plurality of wedges are mechanically inserted within the cavity between the tendon and a wall of the cavity, and pressure is applied to an end of the tendon such that the tendon and the wedges are in interference-fit relationship with the cavity. A compression mechanism is used having a cylindrical member and a plunger extending in a channel of the cylindrical member. The wedges are attached to the cylindrical member and the cylindrical member is moved toward the cavity such that the wedges enter a space between the tendon and the wall of the cavity. The plunger applies a compressive force to the end of the tendon when the end of the tendon is in the channel of the cylindrical member.
U.S. Pat. No. 5,755,065, issued on May 26, 1998 to the present inventor, discloses a post-tension system including an anchor member having a tendon-receiving interior passageway, a tendon extending through the passageway, a pair of wedges interposed between the anchor member and the tendon in the interior passageway, and a spring received by one end of the anchor member so as to be in compressive relationship with the pair of wedges so as to urge the pair of wedges in a direction toward an opposite end of the anchor member. A cap member is affixed to one end of the anchor member and extends over an end of the tendon. The spring is interposed between the cap and the plurality of wedges. The spring is affixed to an interior shoulder on the cap member. A seal is interposed between an exterior surface of a sheathed portion of the tendon and an interior surface of a tubular extension formed in an encapsulation around the anchor.
However, these methods do not address the formation of an anchor with a sheathing lock. Sheathing locks were invented so as to retain the sheathing of a tendon within the anchor so as to prevent the shrinkage of the sheathing while post-tensioning. The present inventor has filed various patent applications pertaining to different sheathing locks: U.S. patent application Ser. No. 11/861,185, filed on Sep. 25, 2007, entitled “Apparatus for Preventing Shrinking of a Sheathing Over a Tendon”; U.S. patent application Ser. No. 11/933,029, filed on Oct. 31, 2007, entitled “Shrinkage Preventing Device for the Sheathing if a Tendon”; U.S. patent application Ser. No. 11/933,041, filed on Oct. 31, 2007, entitled “Shrinkage Preventing Apparatus for the Sheathing of a Tendon”; U.S. patent application Ser. No. 11/950,295, filed on Dec. 4, 2007, entitled “Unitary Sheathing Wedge”; U.S. patent application Ser. No. 12/100,066, filed on Apr. 9, 2007, entitled “Sheathing Lock”; U.S. patent application Ser. No. 12/123,432, filed on May 19, 2008, entitled “Sheathing Retaining Clip; and U.S. patent application Ser. No. 12/133,947, filed on Jun. 5, 2008, entitled “Compression Cap Sheathing Lock.” Because current methods for forming dead-end anchors do not address the use of sheathing locks, there is a need for a method for forming a sheathing retaining anchor.
It is an object of the present invention to provide a method for forming a sheathing retaining anchor that retains a tendon within an anchor.
It is another object of the present invention to provide a method for forming a sheathing retaining anchor that retains a sheathing of a tendon within an anchor.
It is another object of the present invention to provide a method for forming a sheathing retaining anchor in which the tendon in installed by compression forces.
It is another object of the present invention to provide a method which eliminates the hand positioning of wedges during such compression forming.
It is still another object of the present invention to provide a method for forming a sheathing retaining anchor which is safe, easy to use, and relatively inexpensive.
It is another object of the present invention to provide a method for forming a sheathing retaining anchor which eliminates any buckling of the end of the strand during compression fitting.
These and other objects and advantages of the present invention will become apparent from a reading of the attached specification and appended claims.